1. Field of the Invention
The present invention generally relates to computer-implemented methods and systems for determining different process windows for a wafer printing process for different reticle designs. Certain embodiments relate to determining a process window for a wafer printing process for each of different reticle designs based on results of detecting defects in each of the different reticle designs using simulated images.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
Lithography is typically one of the most important processes in integrated circuit manufacturing since this is the process in which features are patterned on the wafer. The pattern printed in a resist by lithography is then utilized as a masking layer to transfer the pattern to additional layers on the wafer in subsequent processing steps. Therefore, the pattern that is formed on the wafer during lithography directly affects the features of the integrated circuits that are formed on the wafer. Consequently, defects that are formed on a wafer during lithography may be particularly problematic for the integrated circuit manufacturing process. One of the many ways in which defects may be formed on the patterned wafer during lithography is by transfer of defects that are present on the reticle to the wafer. Therefore, detection and correction of defects on the reticle such as unwanted particulate or other matter is performed rather stringently to prevent as many defects on the reticle from being transferred to the wafer during lithography.
However, as the dimensions of integrated circuits decrease and the patterns being transferred from the reticle to the wafer become more complex, defects or marginalities in the features formed on the reticle become increasingly important. In particular, if the pattern is not formed accurately on the reticle, such discrepancies increasingly produce defects on the wafer as the dimensions of the pattern decrease and the complexity of the pattern increases. In addition, marginalities in the reticle design may cause the design to print incorrectly on the wafer. Therefore, significant efforts have beet devoted to methods and systems that can be used to detect problems in the pattern on the reticle or in the design that will cause problems on the wafer. These efforts are relatively complex and difficult due, at least in part, to the fact that not all discrepancies or marginalities in the pattern formed on the reticle (as compared to the ideal pattern) will cause errors on the wafer that will adversely affect the integrated circuit. In other words, some errors in the pattern formed on the reticle may not produce defects on the wafer at all or may produce defects on the wafer that will not reduce the performance characteristics of the integrated circuit. Therefore, one challenge of many in developing adequate methods and systems for qualifying a reticle pattern is to discriminate between pattern defects or marginalities that “matter” and those that do not.
One way to check a reticle pattern before the reticle is fabricated is design rule checking (DRC). However, conventional DRC operates only at the nominal process conditions, or at most, at a limited number of process conditions and/or at a limited number of points within the device. Other software based methods for detecting design pattern defects prior to fabrication of the reticle have been proposed, and one such method is described in U.S. Patent Application Publication No. 2003/0119216A1 by Weed, which is incorporated by reference as if fully set forth herein. However, this method is designed to determine only the best focus and exposure settings and not to explore the full range of the process window conditions available for each design. Another method described in U.S. Pat. No. 6,373,975 to Bula et al., which is incorporated by reference as if fully set forth herein, runs simulations only to test for specific design rule violations and does not compare full chip simulated images to a reference to detect arbitrary defects.
Therefore, such software methods have several disadvantages. In particular, these software methods do not examine the full range of process window conditions thereby possibly failing to detect process window marginalities and missing potential defects. In addition, these methods do not determine the exact focus and exposure conditions under which defects will occur thereby preventing the complete optimization of the design. The lack of complete process window information also limits the ability to implement advanced process control techniques for critical dimension control across all critical features on the device.
Accordingly, it would be desirable to develop methods and systems that can detect reticle design defects or marginalities within an entire chip and across a range of process conditions such as focus and exposure before the reticle is manufactured to reduce the cost of fabricating a reticle that is qualified for use in integrated circuit manufacturing and to reduce the time involved in fabricating a reticle that passes qualification for integrated circuit manufacturing. Additionally, it would be desirable to develop methods and systems that can be used to determine different process windows for a wafer printing process for different reticle designs.